One of the earliest and most delightful memories of all my life is lying on my back in the driveway of our family house in Oakland, watching the summer clouds drift across the sky while my mother hung out the clothes to dry and told me stories.

The driveway seems small and, well, limited now, and I have to squeeze between the cars and the side of the house to pass through. But when I was 3, it all seemed an enormous space in which a child's mind could roam. The driveway ... the vast afternoon sky ... my mother's endless stories--it was a wonderful, magical, summer-sky-castle world to which I have often wandered back in my daydreams. Which is why, I imagine, Umberto Eco is one of my favorite novelists.

Eco is the consummate storyteller, with a talent for suspense and intrigue that rivals an Arthur Conan Doyle or an Alexander Dumas.

In his first novel, The Name of the Rose, he gave us a murder mystery in a 14th-century northern Italian Franciscan abbey. Then in Foucault's Pendulum, it was the secret of the Templar Knights and the search for the Rosy-Cross, one of the shrouded icons of Christendom.

Now, in The Island of the Day Before, Eco writes about the race of European nations to find the Holy Grail of the Renaissance World: the determination of longitude while at sea. (To know where one lay along the east-west plane was to be able to master the oceans, and to master the oceans was to be able to conquer the world.)

The Island of the Day Before begins with the unhappy situation of Roberto della Griva, a member of the Italian landed gentry whose ship has been wrecked while on route through uncharted Southern Hemisphere waters in 1643. Roberto drifts at sea on a piece of flotsam until he comes to a second ship, the Daphne, apparently abandoned by its crew, anchored just outside the coral reef of a beautiful island.

Boarding the Daphne, Roberto finds himself trapped. He cannot swim, and the crew has taken the ship's only boat, so he cannot reach the island so tantalizingly close. Roberto, we learn, took his journey in the employ of France's powerful Cardinal Mazarin, spying on the efforts of a Dutch scientist to uncover the longitudinal secret.

And so the book moves both forward and backward in time, as Roberto moves through the labyrinth below decks on the Daphne in an effort to find a way to leave it, and as he reminiscences on the life that brought him to the ship in the first place.

Or, at least, that's the best thumbnail synopsis I can give. Eco's novels can't be understood by reducing them to an outline. His stories, like my mother's, are really just an excuse to daydream.

No matter how compelling the drama, no matter how difficult the situation, he is more than likely to stop in the middle of a great chase and ponder some enigma of the ages, taking you back or forward a thousand or a million years in time, pondering the face or the fate of the universe, looking with wonder into the Eye of God:

[Roberto] went on to recall other rustic delicacies. There were the pies stuffed with little birds, hares, and pheasants, as if to affirm that there can be many worlds, one next to the other or a world within a world. But his mother also made those cakes known as "German-style," with seven layers or stripes of fruit partitioned with butter, sugar, and cinnamon. And from that idea he went on to envision a salted cake, where amid various strata of pastry he put first one of ham, then one of sliced hard-boiled egg, then one of green vegetable. And this led Roberto to think that the Universe could be a pan in which different stories were cooking at the same time, each at its own rate but perhaps all with the same characters. And as the eggs that are below in a pie have no notion of what is happening, beyond their layer of pastry, to their fellow eggs or to the ham above them, so in one stratum of the Universe one Roberto could not know what the other was doing.

Like a little child, you trot along with Eco the teacher, and when he is finished, he will scratch his balding head and say, "Oh, now where was I?" and plunge you back into the thick of things, and the result is like alternately lying on your back and floating in the ocean and then sucking in your breath--quick, now!--as you are snatched down by arms and legs into the water's depths. A little thrilling, yes?

As always, Eco drops you whole into the times and attitudes of the period in which he is writing--this time Western Europe of the turbulent mid-1600s--and he has a remarkable, remarkable gift of getting you to see a world and society not through your own eyes but through the eyes of those who are living there.

Where was he on those dreary, sleepy April afternoons when I couldn't tell 1776 from 1492, and when I was getting Hastings and Cold Harbor horribly confused and, frankly, couldn't have cared less? Eco, one feels, would have had swords flashing and blood flowing all about the classroom, with A's earned all around.

And so he gives us the intrigues of the 17th-century European powers--the jockeying of the nations that soon came to dominate and shape our modern world--in a way that makes you understand their day as well as ours. And he gives us, again, the difficult, bloody birth of the twins Science and Reason and the attempts by the church to smother them as they emerged from the womb. And he gives us all the tricks and fits and starts that scientists and mariners used to determine where they lay along the ocean floor, including something that involved the use of a mysterious Powder of Sympathy and a wounded dog that, um, maybe you might want to skip breakfast before reading.

But the sieges and the struggles and the experiments and the political/social/religious debates leave us bound to the earth like Prometheus, and that is not Eco's intention. Before we can get our battle gear all strapped on, he has us soaring, swimming in the clouds again, teasing us, tantalizing us with thoughts of what is ever out of our reach, always on the other side.

The island of The Island of the Day Before is the book's greatest dream of all. It lies on the 180th meridian, that arbitrary line that peels the earth in two, leaving today on one side and yesterday on the other.

Its significance is explained in a crucial dialogue between Roberto and Father Caspar Wanderdrossel, a German priest:
A thought suddenly arrested Roberto. "And that is not all! You make me realize that if at that same instant I were on the line of the meridian, it would be midnight on the dot, but if I looked to the west, I would see the midnight of Friday and if I looked to the east, I would see the midnight of Thursday. Holy God! ... Forgive me, Father, but this is something miraculous.'

"...But the great miracle is that there is no miracle!" [Father Caspar replies.] "All was foreseen ab initio. ... You know what to the sailors of Magellan happened when they finished their voyage around the world, as Peter Martyr tells? They came back and thought it was a day earlier and instead it was a day later, and they believed God had punished them by taking from them a day, because they had not every Friday holy fasting observed. On the contrary, it was very natural: they had traveled from east to west. If from America towards Asia you sail, you lose one day; if in the opposite direction you sail, you gain a day: this is why [my ship] followed the route of Asia, and your stupid ship the way of America. You are now a day younger than me. Is that not to laugh?"

On the island, Father Caspar seeks literal, scientific proof for the biblical story of the flood, theorizing that there was enough water to cover the earth because God came to the 180th meridian, reached across the line, and borrowed water that had existed in yesterday's earth.

Roberto, the lover and pseudo-philosopher, believes that his beloved has been shipwrecked on the island, and if he can only manage to swim over from the ship, he will enter yesterday, and thus be there in time to save her before she dies.

Hmmmmm. Something like those mind-teasing theories enfolded within the Terminator or 12 Monkeys movies, but a lot more intellectually stimulating.

Eco has a large international corps of fans and followers, one of whom has created a fine World Wide Web page for the novelist/essayist/professor/philosopher that collects his writings, reviews of his books and other related thoughts. But though The Name of the Rose was made into a Hollywood movie--complete with Sean Connery in the starring role--Umberto Eco is not a writer for today's pop culture. He makes you stop and think, and that's something there's precious little being done of these days.

The Island of the Day Before, by Umberto Eco; Harcourt Brace; 513 pages; $25 cloth.